The invention concerns a device for attaching the stator vanes of an axial compressor to an external housing. The device is particularly suitable for the active control of the clearance between the rotor and the stator. The stator vanes are fastened to an inner casing of the housing formed by at least one cylindrical ferrule which, in turn, is supported by fastening means on an internal wall of an outer casing. The space between the two casings is traversed by air from a stage of the compressor.
The nonsimultaneous heating and cooling of the different elements of a compressor make it difficult to control the clearance between the rotor and the stator. In effect, the vane disks of the rotor are thermally protected against the flow of compressed air so as to not attain the temperature of the casing supporting the stator vanes. It is known by engine designers to control the temperature of the outer casing carrying the stator vanes.
To accomplish this temperature control and to prevent the transmission of the heat of the compressed air to the outer casing, the stator vanes have been mounted on an inner casing made of a material having a low coefficient of thermal expansion, and suspended from the outer casing by fastening means.
The control of heat exchanged between the inner casing and the outer casing, made of a conventional material, is accomplished by the ventilation of the outer casing and of the space between the two casings.
French Pat. No. 2,482,661 discloses a compressor housing consisting of an outer casing with a plurality of ventilator tubes on its exterior surface and an inner casing, formed by annular segments, to which the stator vanes are fastened. The inner casing carries, facing the outer casing, a number of flanges forming an axially protruding edge to cooperate with radial raised edges of a corresponding shape provided on the inner face of the outer casing. The annular segments are held in place by a band with tongues preventing their circumferential displacement.
British Pat. No. 2,019,954 describes a compressor housing having annular, coaxial outer and inner casings. The inner casing carries the radially inwardly directed stator vanes and a plurality of projections extending in the outward direction. These projections cooperate with recesses provided in the outer casing. The inner casing consists of annular members placed one after the other along a longitudinal axis of the outer casing. The projections and the thickening of the zone surrounding their recesses form thermal bridges permitting the control of the thermal expansion or contraction of the inner casing in the radial direction.
In these known configurations, the stator vanes, together with the friction bands insuring the tightness of the blades of the rotor vanes, are fastened to the inner casing, of which they are an integral part. It is therefore difficult to gain access to the stator for the replacement of damaged vanes or friction bands.